This invention relates to a double-seat electromagnetic valve which is simple in structure and excellent in oiltightness.
A double-seat electromagnetic valve is known e.g. by Japanese Patent Publication No. 49-10371, which comprises a control plunger arranged in a valve casing, and a valve body displaceable in response to the control plunger and being disposed to selectively assume a first seated position wherein a pressure medium-feeding port is connected to a load-connecting port, and a second seated position wherein the load-connecting port is connected to a reservoir port connected to a return passage.
According to this conventional electromagnetic valve, operating fluid pressure acts upon the valve body interposed between two opposite valve seats at its one side directly, and at its other side via the control plunger, at the same time in such a manner that the two operating fluid pressures are equilibrated with each other. In an embodiment of the conventional electromagnetic valve, a weak spring is used to urge the valve body to close a valve bore. The valve can thus be closed and opened with high responsiveness.
With this arrangement, however, a passageway has to be formed in the valve casing to feed the operating fluid to the control plunger. Furthermore, high oiltightness has to be provided between a cavity within which the control plunger is arranged and which is supplied with the operating fluid under a high pressure, and the aforementioned return passage in which the operating fluid under a low pressure flows. A partition member, which separates the cavity and the return passage from each other, however, is formed therein with a through hole which is penetrated by a push rod secured to the control plunger and urging the valve body to displace same. Since the push rod should smoothly move in the partition member, the machining operation has to be performed with high precision accuracy so as to satisfy both of the requirements of oiltightness and smooth movement of the push rod.